Delignification of Miscanthus by Extraction

Abstract

Removal of lignin from miscanthus liberates cellulose and hemicellulose for hydrolysis to obtain sugars that can subsequently be fermented to ethanol or butanol. Extraction of lignin from raw miscanthus at 70°C is feasible when the extracting solvent contains a base (Ethylenediamine, EDA) mixed with an organic solvent or a mildly hydrophobic ionic liquid. A 50–50 (by weight) mixture of EDA and ethylene glycol removes 75% of the lignin from raw miscanthus when the weight ratio of solvent to miscanthus is 10:1. At the same ratio of solvent to miscanthus, a 10–90 (by weight) mixture of EDA and ionic liquid, 1-ethyl-3-methylimidazolium tosylate ([Emim][Ts]) removes 60% of the lignin. These results suggest that it may be possible to delignify miscanthus by extraction at moderate temperature and atmospheric pressure.

Keywords:

• delignification
• ethylenediamine
• ionic liquids
• miscanthus

ACKNOWLEDGEMENTS

The authors are grateful to the Energy Biosciences Institute (EBI) of UC Berkeley for financial support, to Stefan Bauer and Ana Ibanez for help with analytical methods, and to Sean Dee for useful discussions.

Notes

Extractables include: pectins, tannins, and salts. The solvent used for this extraction is 1:1 volume ratio of ethanol and water. Uncertainty (%) for cellulose and hemicellulose is ±1.5, for lignin it is ±3 while for extractives and ash it is ±1.

[Emim][Ts] is 1- ethyl-3-methylimidazolium tosylate; [Bmim][Dmp] is 1-butyl-3-methylimidazolium dimethylphosphate; [Nmpip][Ac] is N-methyl piperidnium acetate.

Numbers 1–6 refer to solvent mixtures shown in Table 2. Uncertainty (%) for cellulose and hemicellulose content is ±1.5, for lignin it is ±3; and for ashes and extractive it is ±1.